This invention relates to a vapor phase process for the selective disproportionation of fluorodichloromethane (CHCl.sub.2 F) to difluorochloromethane (CHClF.sub.2) and chloroform (CHCl.sub.3) using a solid catalyst of an activated mixture of iron oxide and rare earth oxides.
Generally, fluorinated haloalkanes are produced commercially by liquid phase reaction of anhydrous hydrogen fluoride (HF) with chloroalkanes in the presence of a catalyst as disclosed in Daudt et al., U.S. Pat. Nos. 2,005,705 and 2,005,708. This reaction usually occurs at superatmospheric pressure and is illustrated by the following equation using chloroform as the representative haloalkane: EQU XHF+CHCl.sub.3 .fwdarw.CHCl.sub.3-X F.sub.X +XHCl
antimony PA1 chloride
wherein X=1 to 3. A mixture of products is obtained, the amount of each product produced depends on process conditions and feed ratios. It is not possible, however, to completely avoid the production of undesirable products through control of process parameters. In the above illustration trifluoromethane (CHF.sub.3) is an undesired by-product with a vapor pressure which is too high for significant commercial use; its fluorine values are normally wasted.
The conventional process used to produce fluorinated haloalkanes employs anhydrous HF, a particularly corrosive chemical which is very hazardous to handle. Also, hydrochloric acid (HCl) is a by-product and must be disposed of, either by considerable purification to eliminate residual halocarbons prior to sale, or by neutralization and disposal at significant expense and environmental risk. Finally, the antimony-based catalyst eventually loses both activity and selectivity and must be disposed of with extreme caution because of environmental concerns related particularly to possible contamination of surface and subsurface waters.
French Patent No. 1,422,476 describes a catalyst for hydrofluorination of chlorocarbons to a range of fluorinated products. For example, anhydrous HF is reacted with chloroform in the vapor phase over a catalyst of iron and rare earth oxides to produce CHCl.sub.2 F, CHClF.sub.2, CHF.sub.3 and hydrochloric acid.
U.S. Pat. No. 3,087,967 discloses the conversion of monohydrofluorochloromethanes with one or two fluorine atoms using an activated alumina catalyst. The process proceeds to high conversions of CHF.sub.3 with little conversion of CHCl.sub.2 F and CHClF.sub.2.
The present invention provides a process whereby the product CHClF.sub.2, widely used as a commercial refrigerant and for other commercial purposes, can be manufactured efficiently and selectively under mild conditions. In addition, hazards in handling and the need for strict environmental controls imposed by the use of HF and the recovery and disposal of HC1 and the antimony catalyst are avoided.
More specifically, the object of the present invention is to produce CHClF.sub.2 selectively and efficiently by an acid-free process, while using a catalyst whose eventual disposal poses little or no difficulty or environmental problems.